During the past years, with the increase in price of fossil fuels, the interest in many aspects related to the processing of the fossil fuels has increased. In addition, there is an increased interest in producing more efficient and reliable motors, machines, turbines, compressors, etc. to facilitate a better production and distribution of oil and gas based products.
One such field generally relates to fluid transport systems and, more particularly, to an electrical machine to move fluids through a pipeline. For example, fluids are transported from on-shore or offshore locations to processing plants for subsequent use. There are many type of fluids that need to be transported between different locations. One such fluid may be a highly corrosive gas. In other applications, fluid transport is used in hydrocarbon processing industries and chemical industries, and to facilitate distribution to end-users. At least some fluid transport stations use machinery, such as compressors, fans and/or pumps that are driven by gas turbines. Some of these turbines drive the associated fluid transport apparatus via a gearbox that either increases or decreases a gas turbine output drive shaft speed to a predetermined apparatus drive shaft speed. Electrical machines (i.e., electrically-powered drive motors, or electric drives) may be advantageous over mechanical drives (i.e., gas turbines) in operational flexibility (variable speed for example), maintainability, lower capital cost and lower operational cost, better efficiency and environmental compatibility.
Also, electric drives are generally simpler in construction than mechanical drives, generally require a smaller foot print, may be easier to integrate with the fluid transport apparatus, may eliminate the need for a gearbox, and/or may be more reliable than mechanical drives. However, systems using electric drives generate heat via the drive components, within the stators for example, and may require supplemental systems to facilitate heat removal. For example, some electric drives use the fluid being transported as the primary heat transfer medium and channel the fluid through and around the stator. However, in some cases, the fluid being transported may have aggressive constituents or impurities which may adversely affect the efficiency of the components of the stator. For example an acid fluid being transported negatively affects the copper components of the stator.
For these reasons, a traditional electric machine may place the stator of the machine inside an enclosure that isolates the stator from the rotor as disclosed in Kaminski et al. (U.S. Pat. No. 7,508,101, the entire content of which is incorporated herein by reference) and Kaminski et al. (U.S. Pat. No. 7,579,724, the entire content of which is incorporated herein by reference). Oil may be provided inside the enclosure to maintain the stator in an oil environment that does not damage the copper or other components and also to remove the heat from the stator while the transported fluid contacts only the rotor. The enclosure has part of the walls made by metal and one wall, between the stator and the rotor, made of a non-metallic material, as known in the art.
A problem with the traditional electrical machines is the thermal stress/strain applied to the non-metallic wall during the operation of the machine. If the thermal stress/strain between the metal walls and the non-metallic wall is significant, the non-metallic part may break, which results in the oil being released from the enclosure and damaging the machine. The thermal stress/strain is generated when the machine is operational and its temperature increases from the environment temperature (which may be around 20° C.) to the operational temperature (which may be in the 80 to 150° C. range). Another factor that contributes to the thermal stress is the difference in the coefficients of thermal expansion of the metal wall and the non-metallic wall as it is known that a metal has, in general, a coefficient of thermal expansion three times larger than a non-metallic part. Thus, while operating, the metal walls expand more than the non-metallic wall, which may result in a failure of the non-metallic wall due to the stress/strain applied by the metal walls.
Accordingly, it would be desirable to provide systems and methods that prevent the strain of the non-metallic wall of the enclosure.